Kipp&Zonen UVS-E-T UV Radiometers - Manual (Page 17)

17
The solar zenith angles,
Θ
0
, are varied between 0° and
85° (using steps of 5°) and the Ozone column
densities, [O
3
] are varied between 200 Dobson Units
(DU) and 500 DU (using steps of 10 DU), yielding 18 x
31 = 558 conversion factors. If UV irradiances have to
be measured with broad-band UV radiometer under
exceptional conditions, it is recommended to calculate
new conversion factors using model parameters that
are representative for the exceptional condition (e.g.
snow-covered land surface at a location which is
mostly snow -free).
4.2
ADJUSTMENT STEP:
UVIATOR CORRECTION METHOD
To obtain the most accurate UV irradiances using
broad band UV radiometers, the readings (“raw
radiometer output”) must be multiplied with the
adjustment factor,
χ. This is a combined correction
factor, composed of the radiometric calibration factor,
ρ, and the conversion factor, γ, i.e. χ=1/(ρ•γ).
The UVIATOR program performs the required selection
of the appropriate conversion factor automatically and
corrects an instantaneous UVS measurement
according to the conditions at the time and location of
the measurement. For the selection of the conversion
factor, the parameters
Θ
0
and O
3
have to be
determined according to the measurement conditions
at the time of the UV radiometer reading.
The UVIATOR program calculates the solar zenith
angle,
Θ
0
, for each measurement as a function of the
measurement location (latitude and longitude) and the
GMT of the reading. The total Ozone column density,
O
3
, is automatically retrieved from the OMI or TOMS
satellite data archives. Note, that TOMS data are daily
mean values only. UVIATOR offers plug-ins to allow
the use of other Ozone column observation data, such
as from the Kipp & Zonen Brewer.